Internal combustion engine-powered vehicles require transmissions because of the physics of the internal combustion engine. A rotation speed of an output shaft and/or flywheel of an engine has a maximum revolutions per minute (“RPM”) value, known as redline, above which the engine cannot operate without risking damage to the engine. The transmission allows the gear ratio between the engine and drive wheels to change as the vehicle speeds up and slows down so that the engine stays below redline and near the RPM band of its best performance. In a manual transmission, various gear ratios are achieved by engaging different sets of gears coupled to the drive shaft by a driver operating a shifter. A clutch mechanically couples and decouples an output shaft of the engine to an input shaft of the manual transmission. Disengaging the clutch decouples the shafts and allows the driver to engage and disengage different sets of gears by operating the shifter.
FIG. 1 illustrates an exemplary manual transmission and clutch mechanism in accordance with the prior art. As used herein, a clutch mechanism collectively refers to a slave cylinder, master cylinder, and clutch. There are different clutch mechanism designs, but many are based on one or more friction discs, pressed tightly against a flywheel using one or more springs, for example a diaphragm spring. The one or more friction discs and flywheel, shown in phantom as block 6, are held within a bell housing 16. The flywheel is operably connected with an output shaft of the engine 2 and the one or more friction discs are operably connected with an input shaft of the transmission 4. Friction clutches are mainly actuated through four techniques: mechanically, whereby the clutch is actuated by a lever or pedal connected to the friction clutch through compound linkages and operated by hand or foot; pneumatically, whereby air pressure is used to actuate valves and pistons to engage the clutch while disengagement is achieved through spring force; hydraulically, whereby hydraulic fluid is used to exert pressure on hydraulic valves and pistons to actuate the clutch; and electrically, whereby compound linkages and mechanical actuation are replaced with electromagnets and/or solenoids.
The clutch mechanism shown in FIG. 1 is a hydraulically actuated friction clutch. A slave cylinder 10 is connected to the bell housing 16, and when actuated operates a bearing via a throw-out lever 18 to release a diaphragm spring and disengage the clutch (i.e., allow the one or more friction discs to separate from the flywheel). The slave cylinder 10 is actuated by hydraulic fluid urged into the slave cylinder 10 to push a piston connected with a shaft outward of the slave cylinder housing. The hydraulic fluid is urged into the slave cylinder 10 by a master cylinder 8 connected with the slave cylinder 10 through a first hydraulic line, which as shown includes a flexible hydraulic hose 22 connected with a rigid hydraulic line 26. The master cylinder 8 is connected to a hydraulic fluid reservoir 12 for replenishing hydraulic fluid by a second hydraulic line 20. A clutch pedal 14 is disposed in a cabin of the vehicle so as to be operable by a driver. The clutch pedal 14 of FIG. 1 is merely exemplary. Myriad different configurations and mechanical means exist for actuating a clutch pedal. As shown, when the clutch pedal 14 is depressed, a piston within the master cylinder is urged inward by a shaft 28 actuated with the clutch pedal 14, forcing hydraulic fluid into the flexible hydraulic hose 22 to actuate the slave cylinder 10. When the clutch pedal 14 is released, a spring 24 urges the clutch pedal 14 away from the master cylinder 8 and the hydraulic fluid is drawn and/or urged back into the master cylinder 8, drawing and/or urging the piston and shaft of the slave cylinder 10 back into the slave cylinder housing and actuating the throw-out lever 18 so that the diaphragm spring applies force to engage the clutch.
As mentioned above, an engine is at risk of damage when operating above redline. An engine can also be at risk of damage if the RPMs of the engine increase dramatically in a short period of time. One or both situations may occur under a number of different operational circumstances, many of which result from driver error. For example, where a driver operating an engine at an engine speed approaching redline disengages the clutch to shift gear ratios, but mistakenly selects a lower gear ratio (e.g., shifts from third gear to second gear). When the driver engages the clutch, the engine speed will accelerate rapidly and beyond redline, likely causing engine damage.